Reflex klystrons



1960 TADAKUN! FUJH 2,950,415

REFLEX KLYSTRONS Filed April 13, 1959 Invenior T FUJII A Horney i atent Fire i atented Aug.

REFLEX KLYSTRONS Tadalmni Fujii, Tokyo, Japan, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Apr. 13, 1959, Ser. No. 806,083

Claims priority, application Japan Apr. 15, 1958 1 Claim. (Cl. 315-518) With the conventional reflex klystrons, an electric beam in passing through the modulation gap in the cavity resonator undergoes velocity modulation before entering into a retarding field and then it is reflected back to the modulation gap again.

in this case, the bunching action takes place, causing a density modulated component to be produced in the beam, which will excite said resonator.

However, as the frequency of oscillation becomes higher and reaches the millimeter wavelength region (that is, 30,000300,000 mc.), the loss in each part of the circuit increases rapidly with the result that an electron beam with extremely small diameter and high electron flow density has to pass through an extremely small gap in the cavity resonator. When a grid is installed in the modulation gap, the grid is locally heated by the bombardment of electrons and dissipation of heat becomes difiicult.

In particular, in the case of reflex klystron electrons which have passed through the modulation gap without being interrupted by the grid mesh wires return to the same modulation gap to heat said grid mesh wires. Consequently, assuming that the electron accelerating voltage, diameter of the grid mesh wire, and the diameter of the modulation gap are constant, the grid mesh wire in the reflex klystron will be more heated than that in the straight-path type klystron. This phenomenon presents a critical problem for the reflex klystron when used in the millimeter-wave region inasmuch as it becomes more pronounced with an increase in frequency.

An object of the present invention is the provision of an improved reflex klystron which can be utilized in the millimeter wavelength range and which eliminates defects commonly found in conventional reflex klystron oscillators.

Another object of this type of reflex klystron is to prevent overheating of the modulation grid mesh wires produced by the returning electron beam under the infiuence of the retarding electric field in the klystron which tends to be aggravated with an increase in frequency.

A further object of the present invention is to avoid the hysteresis phenomenon appearing in the oscillation mode pattern due to the multiple transit of electrons that otherwise would be produced.

A still further object of the present invention is that the construction of the annular catcher gap with its comparatively large surface area for the reception of an electron beam results not only in preventing overheating and proper dissipation of heat, but also facilitates the tuning of the klystron to resonance which is accomplished by varying the space of this gap.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 shows the principles of the reflex klystron for millimeter wave use in accordance with this invention; and

Fig. 2 illustrates the distribution of the H.-F. electric field intensity in the radial direction within the H.-F. excitation cavity resonator.

Referring now to Fig. 1, 1 denotes an electron gun, 2 an electron beam emitted from 1, 3 an H.-F. excitation cavity resonator, 4 a buncher cavity situated in the middle of said resonator, 5 a repeller electrode, 6 an orbit followed by the electron beam after passing through the buncher cavity 4, 7 an annular catcher cavity gap installed in the cavity resonator 3, and 8 denotes an output waveguide.

The electron beam 2 emitted from the electron gun 1 in passing through the buncher cavity 4 undergoes velocity modulation by an H.-F. field created in said cavity 4 by resonance of the resonator 3. This electron beam reaches the catcher cavity 7 following the path 6 under the influence of a retarding field created by the repeller electrode which is maintained at negative potential with respect to the cathode of the electron gun 1, exciting the resonator 3.

Consequently, the magnitude of the H.-F. electric field intensity as shown at 9 and 11 in Fig. 2 becomes maximum in the buncher and catcher cavity gaps, respectively. The electron beam which has undergone velocity modulation in the buncher cavity 4 will produce a density modulated component by the bunching action on its Way to the catcher cavity 7, with the result that oscillations would be initiated insofar as the electron transit angle between 4 and 7 is set so as to promote radio-frequency oscillations in resonator 3. This radio-frequency output is fed to the external load through the output waveguide 8.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention, as set forth in the objects thereof and in the accompanying claim.

I claim:

A reflex klystron tube comprising an electron beam source aligned along a given axis within said tube, a repeller electrode extending normal to said axis and spaced a predetermined distance from said source, a cavity resonator positioned between said source and said repeller electrode, said cavity resonator having a buncher region concentric with said electron beam, an annular catcher region radially spaced from said buncher region relative to said axis and concentric to said electron beam, and the contour of said repeller electrode being such as to repel the beam emerging from said buncher region and return it to said catcher region.

References Qited in the file of this patent UNITED STATES PATENTS 2,460,332 Bowman-Manifold Feb. 1, 1949 2,468,152 Woodyard Apr. 26, 1949 2,750,531 Sterling June 12, 1956 

